Frame sizing advice: very confused

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Frame sizing advice: very confused

Postby rogerwilco » Tue May 06, 2014 11:24 am

Hey folks,

I'm really confused.

My current ride is an early 90s repco superlite with modern drivetrain (new shimano 105).
Seat tube and top tube are both 56cm CC
90mm quill stem
It feels a little big. Fairly upright riding position, and I have to reach farther than I'd like to get the brake hoods.

Here are my main body measurements:
height: 5'7 (170cm)
actual inseam: 33 inch (crotch to floor)

I know there are many more measurements/fitting required to get a great fit, but for now, I'm just trying to work out whether I should get a new frame, what the right size would be, and whether it's worthwhile doing.

It seems to be that the 'right' frame size for me is probably 53cm CC.

Any and all advice welcome!
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by BNA » Tue May 06, 2014 12:01 pm

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Re: Frame sizing advice: very confused

Postby RonK » Tue May 06, 2014 12:01 pm

Yup, at 5'7'' a 56cm square frame is too big.
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Re: Frame sizing advice: very confused

Postby herzog » Tue May 06, 2014 12:04 pm

Sounds like a potential ballcrusher.

53 sounds about right.
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Re: Frame sizing advice: very confused

Postby Sychen » Tue May 06, 2014 12:29 pm

I'm similar in measurement. I ride a 54cm Cinelli. Wouldn't want to be on a 56cm assuming in the same range.

Depends on the manufacturer... Between 50cm to 54cm tt for someone our height.

I vote new frame time.
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Re: Frame sizing advice: very confused

Postby kb » Tue May 06, 2014 12:49 pm

Same size here. Currently riding a 54 as I don't mind a bit of stretch and my arms are long. 53 would probably fit better though.
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Re: Frame sizing advice: very confused

Postby rogerwilco » Tue May 06, 2014 2:25 pm

Cool, that really helps.

I'm considering this frame http://www.bicycles.net.au/forums/viewtopic.php?f=25&t=68703
but it is perhaps a little small.

A longer stem could remedy, but I'd rather not... I want to maintain a roughly period correct aesthetic, so I currently have a very nice Nitto pearl quill stem paired with Nitto B105 drop bars. Not the cheapest stem to be replacing...

I guess it's always going to be a bit of a gamble with this kind of build.
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Re: Frame sizing advice: very confused

Postby Nikolai » Tue May 06, 2014 9:11 pm

rogerwilco wrote:but it is perhaps a little small.


If it turns out to be too small, and it probably will, you'll end up with 57 stem spacers and may not be able to move your saddle far enough. Keep calm and keep looking.
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Re: Frame sizing advice: very confused

Postby BriP » Wed May 07, 2014 4:40 am

yeah i would be suggesting a 50-53cm frame for your height..


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Re: Frame sizing advice: very confused

Postby Nobody » Wed May 07, 2014 9:13 am

rogerwilco wrote:Seat tube and top tube are both 56cm CC
90mm quill stem
It feels a little big. Fairly upright riding position, and I have to reach farther than I'd like to get the brake hoods.

Here are my main body measurements:
height: 5'7 (170cm)
actual inseam: 33 inch (crotch to floor)

I know there are many more measurements/fitting required to get a great fit, but for now, I'm just trying to work out whether I should get a new frame, what the right size would be, and whether it's worthwhile doing.

It seems to be that the 'right' frame size for me is probably 53cm CC.
In modern styles you are probably looking at a 51 to 52 seat tube with a corresponding ~53 effective top tube (ETT). But since you are chasing retro, chances are the seat tube angle (STA) is going to be less steep than a modern road bike. The actual body plus arm reach a particular ETT gives is dependent on STA and therefore can't be used in isolation. Better to use the "Reach and Stack" method of measurement including stem height which is explained in the thread below.
viewtopic.php?f=12&t=67990

As for getting a more accurate guide as to what ETT to chase, try the calculator below. One problem with this calculator is they don't specify the STA, but I believe it may be 73 degrees. Most road bikes in your size would probably be about 74 degrees.
http://www.competitivecyclist.com/Store ... ID=IB12809
Last edited by Nobody on Wed May 07, 2014 11:55 am, edited 1 time in total.
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Re: Frame sizing advice: very confused

Postby brentono » Wed May 07, 2014 11:14 am

BriP wrote:yeah i would be suggesting a 50-53cm frame for your height..


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Exactly my thoughts, and it would depend on the length of cranks, type of shoe and type of seat.
With these square frames, in steel, most of the play is adjusted by seat height and travel, and stem.
(much different than the modern sloping bar frames, which many have not taken into account)
You should, on average, be able to wrap your hand around the amount of seatpost that is out (as a guide)
Some oldskool tips, and maybe I have an interest, but really just tryin' to help. Hope you can work it out. :)
Maybe I would get somebody to help, and re-check "actual inseam: 33 inch" ... seems high :?:
Cheers
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Re: Frame sizing advice: very confused

Postby metrofarm » Sat Jun 14, 2014 12:09 am

With relation to your original observation that you're a bit more stretched out than you'd like, here's another old rule of thumb - if you're seated and on the hoods the handlebar should be obscuring your front hub as you look down. If you can see the hub then you're probably dealing with too long a top tube, or headstem. But this is just a rule of thumb. Another rule of thumb is that if an old frame fits right and the saddle and stem are positioned correctly then if you place your elbow against the leading edge of the saddle nose and you extend your arm forwards with your fingers stretched out then those fingers will reach about half way down the length of your stem.

I mention these, and they seem to work for me, because with an old frame, perhaps like the superlite, you might find that you don't get proportional changes in the same way that you do with more modern frames - kind of like you get a 19¦21¦23¦25" range of sizes measured by the seat tube with pretty much the same length top tube. But that's probably only on much older frames. At any rate reach seems most important and I would think that somewhere between a 51 and 54 cm top tube would suit you but more likely towards the 51cm end I would think. I'm about your height (actually 175cm with an inseam of 81 (measured hard up against the bone down there and not where the seam on my jeans happens to be :-) and I find 54cm top tube fine, regardless of my actual standover clearance on a bicycle. Of course in the old 'rule of thumb days' a 53 cm frame measured by the seat post, being a 21 inch, would have been deemed to be your size (unless your legs are relatively short). I have a couple of 20.5" frames and they both have top tubes that are 54cm's long. Sorry for the mixed units!

As has been said above, measure your inseam again (use a thin hard backed book jammed up as high as it'll go standing in your bare feet about 30cm apart) and measure off the book. A friend helps with this obviously, but ... at any rate 33 inches is 83.8 cms and that is quite long relative to a 170cm height. But I'm only thinking a couple of cm's here so its not abnormal. :D just a measurement you want to get right for advice that's not in person

A final rule of thumb when fitting a bike: the rider shouldn't look like a 'dog rooting a barrel' when pedalling the darn thing. That's technical description and a vivid image! lol
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